TAC Meeting #1

Ellen M. Price

8 October 2019

Thesis outline

  • Protoplanetary disk chemical evolution
    • Effect of accretion in a viscously-evolving protoplanetary disk
    • Pebble drift with sublimation only
    • Pebble drift + full chemistry
  • Tidally distorted rocky planets
    • Constraining the composition of USP planets in the Kepler sample
    • Shapes of tidally-distorted transits and detectability
    • Analytic Roche theory for modified polytrope planets

Why should we care?

Role of accretion in setting disk chemistry

Goals of accretion simulation

  • Solve for a self-consistent temperature structure of a protoplanetary disk
  • Simulate independent “tracks” of material moving through the disk and the chemistry along those tracks
  • Compare chemistry at 1 Myr to a disk without accretion


  • Use RADMC-3d to find the temperature at all positions in the disk; iterate with solving for surface density $\Sigma$ until convergence
  • Integrate the velocity equations to get the material tracks through the disk
  • For each track, solve chemistry ODE

Methodology: Solving for tracks

Results: Accretion is important!

Publishing this project

We received a favorable referee report that requested a few modifications, which we have almost completed. We plan to resubmit this week.

Limitations of the simulation

  • No vertical transport considered
  • Limited to the disk midplane
  • One dust population, assumed well-mixed with the gas
  • No self-shielding or UV radiation

Upcoming project: Pebble drift and disk chemistry

Adding more detail

(inspired by Henning & Semenov 2013)

Goals of the simulation

  • Simulate a disk with substantial pebble drift
  • Take into account the pebble size distribution and its impact on the disk evolution
  • Propagate gas and grain chemistry through this disk
  • Many other possibilities for improvement!

Challenges: Radiative transfer

  • Radiative transfer is a circular problem
  • Previously overcome with iterative RADMC runs
  • Perhaps there is a better way?

Challenges: Global solve

  • Unlike last project, need to do a global solve for both chemistry and physics because the particle “tracks” cross
  • How should this be accomplished?
    • Do we include the vertical direction?
    • Can we incorporate cylindrical symmetry?

Possible approach

  • Smoothed particle hydrodynamics naturally solves the fluid equations and can be implemented in cylindrical symmetry
  • Flux-limited diffusion for radiative transfer
  • One-fluid approach for dust, pebbles, and gas
  • Chemical quantities advected with the fluid

Plan B: If all else fails...

  • This is very ambitious!
  • If it doesn't work out:
    • Fall back on existing tools, like RADMC
    • Build on old project code

Current progress: Tidally-distorted rocky planets

Goals of these papers

  • First paper: Introduce the computational method, based on Hachisu's self-consistent field method, results for the USP planet KOI-1843.03
  • Second paper: What does the transit of such a planet look like? Could we detect variations from a spherical transit, or are these effects washed out by limb-darkening?
  • Third paper: Analytic Roche theory for these planets


  • Modified self-consistent field method: Added a point-source star to the calculation and used a modified polytrope equation of state
  • Raytracing using Embree and OSPRay software to determine transit shapes

Composition constraints: Fe cores

Composition constraints: FeS cores

Thesis timeline

Timeline draft: Rest of 2019

  • Submit accretion paper (this week)
  • Publish first TDRP paper (working on this)
  • Start first pebble paper (this month)

Timeline draft: 2020

  • Finish first pebble paper and submit (no later than May, but hopefully sooner)
  • Draft the second and third TDRP papers and submit (by end of summer latest)